This invention relates to highly absorbent materials made by chemically modifying the naturally occurring structure of cellulose. Specifically, cellulose is etherified to a sufficiently high degree to produce alkali metal cellulose ethers which are soluble in water and is then modified by grafting to produce highly absorbent insoluble cellulose ether salts.
Cellulose fiber and regenerated cellulose are raw materials for many commercial absorbent products including, for example, such products for absorbing body fluids as catamenial napkins and tampons, diapers and surgical dressings. While, in the main, unmodified cellulose has proven useful in such products, in an effort to improve product quality and economy, the art has searched for improved materials. It was discovered, for example, that alkali metal salts of cellulose ethers such as sodium carboxymethyl cellulose exhibited increased absorption and retention properties for body fluids, these desirable properties increasing with the degree of ether substitution (D.S.). Accordingly, such materials in, of course, insoluble form are useful in products for absorbing body fluids, such teachings being disclosed in U.S. Pat. No. 3,005,456, issued to Graham on Oct. 24, 1961. Further in U.S. Pat. No. 3,589,364 issued to W. L. Dean and G. N. Ferguson on June 29, 1971, there is disclosed a particular form of insoluble, sodium carboxymethyl cellulose having a high degree of substitution of ether groups and insolubilized by wet crosslinking the cellulose using methods such as are described in U.S. Pat. No. 3,241,553, issued to F. H. Steiger on Mar. 22, 1966. In U.S. Pat. No. 3,678,031, still another form of insoluble carboxymethyl cellulose is disclosed having a high degree of substitution, and in this case, insolubilized by an acid and heat treatment. U.S. Pat. No. 3,256,372 to Adams et al. discloses grafting hydrophilic polymers to the cellulose backbone and, in our application Ser. No. 422,627, now U.S. Pat. No. 3,889,678, we disclose still another chemical modification of cellulose whereby a balanced quantity of ionic and nonionic copolymer moieties are grafted to the cellulose backbone and may be grafted to modified forms of cellulose as well.
Each of these references teach modified forms of cellulose which represent great improvements in absorption and retention capacities for body fluids over the properties of unmodified cellulose. Notwithstanding these prior art improvements, the search continues for still better absorbents.